Tube amp head alternative for guitar?

I have a peavey vypyr modeling amp and i want to get that rich sound of a tube amp with out paying a lot. Is there like a pedal with a tube in it that makes that nice sounding distortion. I would like to get away with some money still in my pockets (I'm 15) so i don't want to pay more than 100 dollars for something decent that will get me close to that sound. Any suggestions?